web/captcha.py
author Alexandre Fayolle <alexandre.fayolle@logilab.fr>
Fri, 02 Apr 2010 14:28:43 +0200
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catch and log errors caused by bad json data
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"""Simple captcha library, based on PIL. Monkey patch functions in this module
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if you want something better...
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:organization: Logilab
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:copyright: 2009-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
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:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
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:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
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"""
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__docformat__ = "restructuredtext en"
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from random import randint, choice
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from cStringIO import StringIO
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import Image, ImageFont, ImageDraw, ImageFilter
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from time import time
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from cubicweb import tags
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from cubicweb.web import ProcessFormError, formwidgets as fw
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def pil_captcha(text, fontfile, fontsize):
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    """Generate a captcha image. Return a PIL image object.
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    adapted from http://code.activestate.com/recipes/440588/
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    """
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    # randomly select the foreground color
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    fgcolor = randint(0, 0xffff00)
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    # make the background color the opposite of fgcolor
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    bgcolor = fgcolor ^ 0xffffff
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    # create a font object
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    font = ImageFont.truetype(fontfile, fontsize)
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    # determine dimensions of the text
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    dim = font.getsize(text)
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    # create a new image slightly larger that the text
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    img = Image.new('RGB', (dim[0]+5, dim[1]+5), bgcolor)
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    draw = ImageDraw.Draw(img)
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    # draw 100 random colored boxes on the background
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    x, y = img.size
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    for num in xrange(100):
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        draw.rectangle((randint(0, x), randint(0, y),
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                        randint(0, x), randint(0, y)),
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                       fill=randint(0, 0xffffff))
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    # add the text to the image
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    draw.text((3, 3), text, font=font, fill=fgcolor)
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    img = img.filter(ImageFilter.EDGE_ENHANCE_MORE)
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    return img
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def captcha(fontfile, fontsize, size=5, format='JPEG'):
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    """Generate an arbitrary text, return it together with a buffer containing
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    the captcha image for the text
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    """
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    text = u''.join(choice('QWERTYUOPASDFGHJKLZXCVBNM') for i in range(size))
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    img = pil_captcha(text, fontfile, fontsize)
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    out = StringIO()
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    img.save(out, format)
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    out.seek(0)
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    return text, out
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class CaptchaWidget(fw.TextInput):
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    def render(self, form, field, renderer=None):
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        # t=int(time()*100) to make sure img is not cached
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        src = form._cw.build_url('view', vid='captcha', t=int(time()*100),
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                                 captchakey=field.input_name(form))
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        img = tags.img(src=src, alt=u'captcha')
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        img = u'<div class="captcha">%s</div>' % img
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        return img + super(CaptchaWidget, self).render(form, field, renderer)
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    def process_field_data(self, form, field):
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        captcha = form._cw.get_session_data(field.input_name(form), None,
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                                            pop=True)
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        val = super(CaptchaWidget, self).process_field_data(form, field)
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        if val is None:
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            return val # required will be checked by field
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        if captcha is None:
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            msg = form._cw._('unable to check captcha, please try again')
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            raise ProcessFormError(msg)
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        elif val.lower() != captcha.lower():
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            msg = form._cw._('incorrect captcha value')
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            raise ProcessFormError(msg)
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        return val